Conventional panning procedures to prepare hard coatings generally work with sucrose, but recent advances in panning have allowed the use of other carbohydrate materials to be used in the place of sucrose. Sucrose proves to be detrimental for teeth and causes dental caries due to easy formation of acids. Therefore coatings are nowadays increasingly made of sugar-free compositions.
U.S. Pat. No. 4,127,677 describes a sugarless xylitol-coated chewing gum, which delivers an intense cooling effect and which has a pleasant smooth feel. However the cost of xylitol is quite high and partial replacement of xylitol in the coating would be an advantage.
To obtain good hard coatings, fast even crystallisation must occur during application and drying.
WO 95/07625 describes the advantages of at least partial replacement of xylitol with erythritol in chewing gum coating. In a specific example erythritol and xylitol are used together in a single layer, since both polyols are co-crystallised. Preferably the xylitol portion of the solids in the solution should be about 40% to about 80% xylitol, with the solids in the solution comprising about 20% to about 60% erythritol. However, example 6 demonstrates that the hard coating easily peels from the gum core and it has a slight sandpaper finish. This example demonstrates that application of polyol mixtures in hard coatings is very sensitive to the ratio of the polyols and depends on the kind of polyol applied. Furthermore, the appearance of the coating is sometimes affected by the crystallisation difficulties.
On the other hand sorbitol has been suggested as a substitute for sugar in sugarless preparations. However, it is common general knowledge that sorbitol can be used as an ingredient of the core but difficulties might arise to apply sorbitol in hard coatings, due to its hygroscopic nature. The major drawback of the use of sorbitol is that the resulting coating layers do not show the same crunchiness and crispiness as the conventional sucrose-based coatings.
U.S. Pat. No. 4,238,510 discloses a method for sorbitol coating wherein it is ensured that the sorbitol crystallises. By this method cycles are repeatedly carried out comprising a) application of a first coating syrup containing sorbitol, an adhesion or binder component and a film-forming agent, b) application of a dry dusting powder in the form of a mix comprising sorbitol in a powdered form, a moisture absorbing component, an anti-sticking component and a dispersing agent. It is believed that the crystalline powder acts as a seed crystal for the saturated sorbitol solution. However, the obtained result is not satisfactory since the coating layer is not evenly distributed, and rough surfaces are obtained, while the hard coating is not as crunchy as is obtained with normally employed sugars.
U.S. Pat. No. 4,423,086 describes that hard coatings based on sorbitol can be obtained when applying a coating syrup having a concentration of dry matter comprised between 60 to 85% by weight and the richness of the syrup in sorbitol being greater than 80%, preferably greater than 95%, and still more preferably greater than 99%. On the other hand the sorbitol based coatings are less expensive but lack the important cooling effect of the hard coatings based on xylitol which is giving the pleasant smooth feeling and which is especially desirable for the application of hard coatings of chewing gums. In this respect, sorbitol coatings are improved by the addition of other polyols, which have this important cooling effect.
However U.S. Pat. No. 5,536,511 mentions that it has been difficult in practice to use more than 5% sorbitol in a xylitol panning coating, and at these low levels, sorbitol acts as a crystallisation modifier. These coatings with limited amount of sorbitol lack the cost-effective advantage.
So far sorbitol based hard coatings contain either more than 80% sorbitol, preferably more than 99% sorbitol, or the hard coatings are based on mixtures of sorbitol with other polyols such as xylitol, but then the quantity of sorbitol is practically limited to 5%.
EP 0813817 discloses a process for coating cores with mixtures of sorbitol and other polyols, wherein the concentration of sorbitol is not limited to 5%. The applied process is different from the panning procedures, which are applying solely liquid coating syrups, and consequently the obtained products are different. The sorbitol syrup is applied to a rotating mass of cores and then at least one other polyol is added in a crystalline form. Preferably, the polyol is selected from the group consisting of Isomaltr, xylitol, and erythritol. The crunchiness is at least comparable to that obtained with sucrose. However, the mentioned method requires the addition of the second polyol in crystalline form. Accordingly, a need exists in the market place for a cheap sugarless coating prepared from liquid mixtures of polyols, resulting in a crunchy hard coating, which is well adhered to the gum base.